Force border-radius in Bootstrap to given value, but only when the original value is greater than zero.

_mixins.scss

// Border Radius
@mixin border-radius($value) {

  @if type-of($value) == "list" {
    $new-value: ();

    @each $n in $value {
      $new-value: append($new-value, if($n > 0, 2px, 0));
    }

    $value: $new-value;
  } @else {
    $value: if($value > 0, 2px, 0);
  }

  -webkit-border-radius: $value;
     -moz-border-radius: $value;
          border-radius: $value;
}

// Single Corner Border Radius
@mixin border-top-left-radius($value) {
  @include border-radius($value 0 0 0);
}
@mixin border-top-right-radius($value) {
  @include border-radius(0 $value 0 0);
}
@mixin border-bottom-right-radius($value) {
  @include border-radius(0 0 $value 0);
}
@mixin border-bottom-left-radius($value) {
  @include border-radius(0 0 0 $value);
}

// Single Side Border Radius
@mixin border-top-radius($value) {
  @include border-radius($value $value 0 0);
}
@mixin border-right-radius($value) {
  @include border-radius(0 $value $value 0);
}
@mixin border-bottom-radius($value) {
  @include border-radius(0 0 $value $value);
}
@mixin border-left-radius($value) {
  @include border-radius($value 0 0 $value);
}